1. Field of the Invention
The present invention relates to a telephone device capable of transmitting an on-hold tone to a remote telephone device through a telephone line upon manipulation of an on-hold button. More particularly, the invention relates to a telephone device capable of preventing an on-hold tone played during an on-hold status of the telephone device from being mistakenly detected as a control signal, such as a calling tone (CNG) signal.
2. Description of the Related Art
Conventionally, there has been known a versatile communication device capable of transmitting facsimile data to a remote facsimile device as well as voice communicating with a remote telephone device through a telephone line. The communication devices having a telephone function and a facsimile function can be classified into three types: integral telephone/facsimile types, external attachment types, and parallel connection types. In the integral telephone/facsimile types, a telephone function and a facsimile function are provided in a single device. In the external attachment types, a facsimile device includes an attachment portion for connecting with a separate telephone device. By attaching the telephone device to the facsimile device using the attachment portion, the telephone device becomes connected to a telephone circuit through the facsimile device. In the parallel connection types, a facsimile device and a telephone device use a single telephone line together. When these devices detect the CNG signal, which is a control signal relating to transmission of facsimile data, the connection with the telephone line is changed for facsimile transmission, thus enabling both reception of incoming telephone calls and of facsimile data.
Conventional devices constantly check for reception of control signals such as the above-described CNG signal. Also, the telephone function normally includes a hold feature, wherein a certain melody is played to indicate the on-hold status to the caller. There is a possibility that the on-hold melody can include the same frequency components as the CNG signal or other control signal. For example, the CNG signal has a frequency of 1100 Hz and alternates between an ON condition for 0.5 seconds and an OFF condition for 3.0 seconds. Because the variety of on-hold melodies is ever increasing, it is quite likely that some on-hold melody will include these characteristics of the CNG signal.
If the communication device detects a frequency in an on-hold melody that is the same as the CNG signal or other control signal, then the communication device will mistakenly switch to processes for receiving a facsimile data. There is also a danger that the communication device will be unable to switch out of the facsimile reception mode, even after the on-hold status is released.